Alloy rayon fibers having dispersed therein an amide polymer and a polyacrylic acid salt

ABSTRACT

Alloy fibers having high fluid-holding capacity, and a method for making the same, the alloy fibers being comprised of a matrix of regenerated cellulose having polyvinylpyrrolidone dispersed therein. The polyvinylpyrrolidone may be present in combination with an anionic polymer.

CROSS REFERENCE

This application is a continuation-in-part of my following United Statespatent applications: Ser. No. 309,076, filed Nov. 24, 1972, now U.S.Pat. No. 3,919,385; Ser. No. 530,476, filed Dec. 6, 1974, now U.s. Pat.No. 3,951,889, as a division of my said application Ser. No. 309,076;and Ser. No. 625,445, filed Oct. 24, 1975, now U.S. Pat. No. 4,041,121,as a continuation-in-part of my application Ser. No. 309,290, filed Nov.24, 1972, now abandoned.

This application is also a continuation-in-part of my pendingapplication Ser. No. 629,952 filed Nov. 7, 1975, and my application Ser.No. 741,172 filed Nov. 12, 1976, and now abandoned; the entiredisclosures of those applications are incorporated herein by reference.

The present invention is directed to alloy fibers having highfluid-holding capacity.

Fluid-holding capacity of fibers may be measured by the pellet testdescribed in Example I below or the Syngyna test referred in Example IIIbelow. These tests use a pre-determined mass of fibers maintained underexternal pressure and indicate the amount of water absorbed by thefibers themselves as well as the amount of water retained within theinterstices of the mass.

One aspect of this invention relates to absorbent alloy fibers, eachhaving a matrix of regenerated cellulose and polyvinylpyrrolidoneuniformly dispersed therein, with the regenerated cellulose being themajor portion of the fiber mass. These alloy fibers may be prepared bymixing an aqueous solution of polyvinylpyrrolidone with afilament-forming viscose, shaping the mixture into fibers, coagulatingand regenerating the shaped fibers and thereafter drying the same.Viscose constitutes the major portion of the mixture and the shapedalloy fibers are coagulated and regenerated by known means, andpreferably in an acid bath containing sulfuric acid and sodium sulfate.The acid bath often contains zinc sulfate as well as other coagulationmodifiers as desired.

During the spinning of the viscose into the acid bath, hydrogen ionsdiffuse into the stream of viscose emerging from each spinneret hole.The reaction of the acid with caustic soda in the viscose producessodium sulfate and water; the acid also decomposes xanthate groups. Thepresence of sodium sulfate in the spin bath acts to induce coagulationof the viscose streams owing to dehydration from the interiors of thestreams. Zinc ions in the spin bath act, at least at the surfaces of thestreams, to convert sodium cellulose xanthate of the viscose to zinccellulose zanthate which is decomposed more slowly by the acid andthereby keeps the fiber in more stretchable and orientable condition.Typically the temperature of the acid bath is in the range of about 30°to 65° C. (such as about 50°-55° C.) and the fiber, after passingthrough the acid bath is subjected to a bath of water (or dilute acid)first at a high temperature such as about 80° C. to the boiling point,e.g., about 85°-95° C. and/or to steam, and then to water at a moderatetemperature such as about 35 or 45 to 65° C. In the high temperatureaqueous treatment the fibers may be subjected to stretching, e.g. byabout 50-75%. While for most uses the fibers need not have high strengthproperties, the alloy fibers have been found to retain to a large extentthe physical properties of non-alloy rayon; for instance, using spinningand treatment conditions which gave a non-alloy control having a dry(conditioned) tenacity of about 2.9 g/d, dry elongation of about 20%, adry modulus of about 72 g/d, a wet tenacity of about 1.6, a wetelongation of about 30%, and a wet modulus of 4.8 g/d, an alloy fiber(made from a spinning solution in which the ratio of cellulose topolyvinylpyrrolidone was about 69:31) showed a dry tenacity of about 2.4g/d, a dry elongation of about 17%, a dry modulus of about 66 g/d, a wettenacity of about 1 g/d, a wet elongation of about 27% and a wet modulusof about 4.1 g/d. With lower proportions of polyvinylpyrrolidone thesephysical properties are closer to those of the non-alloy fibers.Typically, the alloy fibers of this invention are not brittle and can becarded under conditions that cause fiber breakdown of more brittle (e.g.cross-linked) fibers. Also they swell to a greater degree in water thanthe non-alloy rayon fibers.

The viscose which is employed in making the alloy fibers of the presentinvention is desirably of a composition as is used in makingconventional regenerated cellulose fibers, e.g. a viscose produced byreacting alkali cellulose with carbon disulfide, with the resultingsodium cellulose xanthate being diluted with aqueous caustic to providethe resulting viscose with a desired cellulose and alkali content. Forexample, the viscose composition may contain cellulose ranging from 3 toabout 12 wt. percent (e.g. 6 to 10%), caustic from about 3 to 12 wt.percent, and carbon disulfide, based on the weight of cellulose fromabout 20 to about 60%. Additives or modifiers may be mixed in theviscose if desired.

The polyvinylpyrrolidone preferably has a high molecular weight, such aswell above 10,000. Very good results have been attained withpolyvinylpyrrolidone of average molecular weight ranging from 100,000 to400,000 and, more desirably, from 160,000 to 360,000, and a preferredK-value of from 50 to 100. The procedure for determining the K-value ofsuch polymers is known in the art, as disclosed in Modern Plastics,1945, No. 3, starting on Page 157. Polyvinylpyrrolidone of desiredcharacter is commercially available, for example, under the designationof K-60 and K-90 from GAF Corporation. Polyvinylpyrrolidone is describedin Encyclopedia of Polymer Science and Technology, published in 1971 byJohn Wiley & Sons, in the article on "N-Vinyl Amide Polymers" in Volume14, pages 239-251.

The polyvinylpyrrolidone may be the sole high polymeric additive in theviscose or it may be used together with other water-soluble (includingaqueous alkali-soluble) high polymers. Preferably these are anionicpolymers such as polymeric acids or salts (e.g. alkali metal salts)thereof, e.g. salts of carboxyalkyl celluloses (such as sodiumcarboxymethyl or carboxyethyl cellulose), salts of polyacrylic acids,(including polyacrylic acid or polymethacrylic acid homopolymer, orcopolymers of acrylic and/or methacrylic acid with each other[e.g.-10:90, 25:75, 50:50:, 75:25 or 90:10 acrylic: methacrylic ratio,one such 10:90 copolymer being the one sold as Acrysol A-41 and othersbeing described in U.S. Pat. No. 4,066,584, or one or more othermonomers such as acrylamide or alkyl acrylates, e.g., ethyl acrylate,salts of copolymers of maleic or itaconic acid with other monomers suchas methyl vinyl ether, or naturally occurring polycarboxylic polymers,such as algin. These materials are preferably dissolved in aqueousmedium before addition to the viscose, the solution being preferablyalkaline, e.g., they may be made with an amount of alkali, such as NaOH,stoichiometrically equivalent to the amount of acidic (e.g., carboxyl)groups of the polymer or with an excess of alkali. Less desirably, thesematerials may be added in acid form (again preferably as aqueoussolutions) and be converted to salt form by the action of the alkalipresent in the viscose. The anionic polymers may be those disclosed inthe art as forming complexes with polyvinylpyrrolidone; see U.S. Pat.No. 2,901,457. Other water-soluble high polymers include substantiallynon-ionic polymers such as starch (which may be added as, say analkaline solution containing some 2-5% of NaOH) or polyvinyl alcohol.

The proportion of polymer added to the viscose should be such as toimpart improved fluid holding capacity to the rayon. Preferably it issuch as to produce fibers whose fluid holding capacity (as measured bythe "Syngyna" test described in Example III below) is at least 5 cc pergram and more, preferably at least 5.5 cc per gram. As will be seenbelow, the practice of this invention has made it possible to attainfluid holding capacities which are well above 6 cc per gram and evenabove 6.5 cc per gram. The fluid holding capacities attained inpreferred forms of the invention are more than 20% better than those offibers spun and processed under the same conditions but in the absenceof the added polymer material; as can be seen from the Examples below,this improvement is often greater than 25%, such as about 30, 40, 50, 60or even 70%.

In general the total proportion of added polyvinylpyrrolidone, alone ortogether with the anionic polymer, is within the range of about 6 to 40%based on the weight of cellulose in the viscose, and more desirably inthe range of about 10 l or 20 to 35%, based on the weight of cellulose.As shown below, higher proportions, e.g. about 50 or 70% may also beused. Expressed in terms of the total of cellulose and added polymer(hereinafter termed "the total") the proportion of added polymer isgenerally in the range of about 7 to 30% such as about 10, 15 or 20%,although higher proportions may be employed. The proportion ofpolyvinylpyrrolidone, when used in combination with anionic polymer, isadvantageously above 1% of the total, preferably above about 2 or 3% ofthe total such as about 5% or more of the total. In one preferred formthe weight ratio of polyvinylpyrrolidone to anionic polymer is at leastabout 10:90, such as about 20:80, 30:70, 50:50, 70:30 or 80:20.

It will be understood that fibers of good fluid-holding capacity may beproduced by the use of the anionic polymer as the sole added polymerwithout the polyvinylpyrrolidone; e.g., one may employ an alkaline saltof a polyacrylic acid (such as, an aklaline sodium salt of acrylic acidor methacrylic acid of homopolymer, or of acrylic acid--methacrylic acidcopolymer, in the acrylic: methacrylic ratios mentioned above) inadmixture with viscose, the proportion of such added polymers being asdescribed above (such as in the range of about 6 to 40%, e.g., 10 or 20to 35%, based on the weight of cellulose).

The polyvinylpyrrolidone described exhibits good solubility in water andaqueous solutions of polyvinylpyrrolidone, with or without addedpolymer, may be incorporated into the viscose at any stage, then blendedand pumped to spinnerets for extrusion. After the spinning, coagulation,and regeneration stages, the shaped continuous tow of filamentsundergoes the usual processing, which may include stretching if desired,and is then dried by conventional means. Generally, before drying, thecontinuous tow of filaments is cut into staple of a desired length. Bythe practice of the invention one can prepare alloy fibers of high fluidholding capacity which do not bond together during drying, even in theabsence of applied finish, and can be subsequently carded with nodifficulty by the manufacturer of articles incorporating such fibers. Toaid in processing one may apply a lubricating finish, preferably of thehydrophilic type, e.g. a nonionic finish such as a Span or Tween(partial higher fatty acid, e.g. lauric, ester of sorbitan or mannitanor a polyoxyethylene derivative thereof) e.g. Span 20 or Tween 20. Suchfinish may be applied as a dilute aqueous dispersion thereof beforedrying. One may also treat the fibers with alkaline solutions toincrease the pH of the dried fiber; treatments with alkaline solutionsare described in some of the Examples and the alkali solution may beblended with the finish. The drying may be effected in any suitablemanner, preferably by evaporating off the water by heat, e.g. in a hotair oven at moderate temperature (such as about 70° C.) or a microwaveoven. Typically drying is effected to such degree as to bring themoisture content of the fibers to about 8 to 20%, such as about 10-13%.

The alloy fibers of the present invention are adapted for use in avariety of articles, such as sanitary menstrual napkins and vaginaltampons, in which high fluid retention is an essential characteristic.In the manufacture of such articles, the alloy fibers necessitate nospecial techniques or equipment and they may be blended with otherfibers which may or may not enhance the absorbent properties of theresulting articles. Fibers with which the alloy fibers of the presentinvention may be blended include, for example, rayon, cotton, chemicallymodified rayon or cotton, cellulose acetate, nylon, polyester, acrylic,polyolefin, etc. Typically a tampon is an elongated cylindrical mass ofcompressed fibers, supplied within a tube which serves as an applicator;see U.S. Pat. Nos. 2,024,218; 2,587,717; 3,005,456; 3,051,177.

The following Examples illustrate the invention further.

EXAMPLE I

Using conventional rayon spinning equipment, aqueous solutions ofpolyvinylpyrrolidone, designated as K-60 (GAF Corporation) and having anaverage molecular weight of about 160,000 and K-value of 50-62, wereseparately injected by a metering pump into a viscose stream during itspassage through a blender and the blend thereafter extruded. During thisthe blend was subjected to high mechanical shearing. The viscosecomposition was 9.0% cellulose, 6.0% sodium hydroxide and 32% (basedupon the weight of the cellulose) carbon disulfide. The viscose ballfall was 56 and its common salt test was 7.

The mixtures of viscose and polyvinylpyrrolidone were extruded through a720 hole spinneret into an aqueous spinning bath consisting of 7.5% byweight of sulfuric acid, 18% by weight of sodium sulfate, and 3.5% byweight of zinc sulfate. After passage through the spinning bath, theresulting continuous tow was washed with water, desulfurized with anaqueous solution of sodium hydrosulfide, washed with water, acidifiedwith an aqueous HC1 solution, and again washed with water. The still wetmultifilament tow was cut into staple fibers and, without any furthertreatment, dried.

The fluid-holding capacity of sample fibers, made with variousapproximate proportions (tabulated in Table I) of cellulose andpolyvinylpyrrolidone in the spinning solution, was determined using thefollowing test procedure.

Sample staple fibers were carded or otherwise well opened and thenconditioned at 75° F. and 58% relative humidity. Two grams of such alloyfibers were placed in a one-inch diameter die, pressed to a thickness of0.127 inch, and maintained in this condition for one minute. Thiscompressed pellet of fibers was removed from the die and placed on aporous plate of a Buchner funnel. The upper surface of the pellet wasthen engaged with a plunger which was mounted for free verticalmovement, the plunger having a diameter of one inch and a weight of 2.4pounds.

The funnel stem was connected by a flexible hose to a dropping bottlefrom which water was introduced into the funnel to wet the pellet offibers. Control over the water flow was exercised by the position of thedropping bottle. After an immersion period of two minutes, the water waspermitted to drain from the fiber pellet for three minutes, after whichthe still wet pellet was removed from the funnel and weighed. One-halfof the weight of water in the sample pellet is a measure of thefluid-holding capacity of the fibers, expressed in cc/g.

The test results of sample fibers, as described above, are set forth inTable I.

EXAMPLE II

A 20% aqueous solution of polyvinylpyrrolidone, designated as K-90 (GAFCorporation) and having an average molecular weight of 360,000 and aK-value of 80-100, was injected into a viscose having a composition asdescribed in Example I, after which the mixture was extruded as acontinuous tow and processed as described above. The relativeproportions of cellulose and polyvinylpyrrolidone in the spinningsolution were 83:17. The resulting fibers had a fluid-holding capacity(tested as in Ex. I) which was 28% higher than conventional regeneratedcellulose fibers.

EXAMPLE III

Aqueous solutions of polyvinylpyrrolidone, designated as K-90 (GAFCorporation) and having an average molecular weight of about 160,000 andK-value of 80-100, were separately injected into a viscose having acomposition as described in Example I. In a manner as described inExample I, the mixtures of viscose and polyvinylpyrrolidone were shapedinto a tow, treated with an aqueous solution containing 1.0% Span 20 andthen cut into staple fibers.

Two and one-half grams of the different fibers prepared as describedabove were separately made into tampons by the following procedure: Thefibers were carded into webs, each having a length of about 6 inches andbeing of variable thickness and width. Each of these webs wasindividually rolled in the direction of its width to provide a six inchroll and a string was looped about the center thereof. Each such rollwas then folded on itself at the string loop and drawn into a 1/2 inchtube within which it was compressed by a clamp and plunger. Aftercompression, the resulting tampons were removed, allowed to stand for aperiod of about 30 minutes during which the tampons recovered to a bulkdensity of about 0.4% cc/g and were then evaluated for their capacity tohold water by the Syngyna Method, as described by G. W. Rapp in a June1958 publication of the Department of Research, Loyola University,Chicago, Illinois. The results of such test are set forth in Table IIfor fibers made with various approximate proportions, as tabulated inTable II of cellulose and polyvinylpyrrolidone in the spinning solution.

EXAMPLE IV

A conventional, non-derivatized viscose, an aqueous solution ofpolyvinylpyrrolidone and a carboxyethyl cellulose (specifically acyanoethylated viscose) were prepared separately. The composition of thenon-derivatized viscose was 9.0% rayon cellulose, 6.0% sodium hydroxideand 32% carbon disulfide, based on the weight of the cellulose. Thisviscose had a ball fall of 56 seconds and its common salt test was 7.

The aqueous solution of polyvinylpyrrolidone was prepared simply bydissolving, in water, polyvinylpyrrolidone K-60.

Cyanoethylated viscose was prepared by premixing 8.25 lbs. of carbondisulfide and 10.75 lbs. acrylonitrile (34% and 45%, respectively, basedon the weight of the cellulose), with the mixture then being chargedinto an evacuated churn by gravity through a valved stainless steelLine. The churn contained a 77 lb. batch of alkali cellulose crumbs andwas kept at a temperature of 15° to 32° C. during a two hour reaction orchurning period. Sufficient water and caustic were added to the churnafter the two hour reaction period to provide a viscose of 8.0%cellulose and 6.0% sodium hydroxide (caustic) based on the weight of theviscose, and 34% carbon disulfide and 45% acrylonitrile based upon theweight of the cellulose, after mixing in the churn for an additional oneand three quarter hours. The resulting cyanoethylated viscose had acommon salt test of 17-21 and a ball fall of 40-50 seconds. Its contentof cellulose derivative recoverable on spinning into, or precipitationby, a sulfuric acid spin bath was about 9%; this 9% value was used tocalculate the proportions of such cellulose derivative (termed "CEC",for carboxyethyl-cellulose) in the Table III.

Using conventional spinning equipment, the alloying materials wereinjected into the non-derivatized viscose as hereafter set forth, withthe resulting mixture being extruded through a 720 hole spinneret intoan aqueous spinning bath consisting of 7.5% by weight of sulfuric acid,18% by weight of sodium sulfate, and 3.5% by weight of zinc sulfate.After passage through the spinning bath, the resulting continuous towwas washed with water, desulfurized, acidified, and again washed withwater in a manner as described in Example I. The still wet tow was cutinto staple fibers which were treated with an aqueous solutioncontaining 0.5% Span 20, dried, carded and then conditioned at 75° F.and 58% relative humidity.

The fluid-holding capacity of sample unalloyed fibers and fiberscontaining the alloying components individually and in combination wasdetermined using the test procedure described in Example I. Theapproximate proportions in the spinning solutions used for the unalloyedand alloyed fibers and the results of such tests are set forth in TableIII.

It will be noted that conventional rayon fibers (Sample A), as producedfrom non-derivatized viscose, exhibit fluid-holding capacities which areless than those of alloy fibers produced from a mixture of conventionalviscose and polyvinylpyrrolidone (Samples E and F) and that thefluid-holding capacities of fibers comprised of non-derivatizedregenerated cellulose alloyed with regenerated cyanoethyl celluloseincrease directly with the regenerated cyanoethyl cellulose content(Samples B, C and D). Significantly, notwithstanding the detrimentaleffects produced when the lower amounts of cyanoethylated viscose areemployed alone as alloying agents, as illustrated by Samples B and C,such derivatized viscose, when combined with polyvinylpyrrolidone, doesprovide for a synergism, as exhibited by the remarkably improvedfluid-holding capacities of the three-component alloy fibers indicatedas Samples G and H.

The terminology "cyanoethylated viscose" as used herein refers to aviscose to which acrylonitrile is added or viscose prepared by thesimultaneous cyanoethylation and xanthation of alkali cellulose. Thelatter procedure is preferred from the standpoint of economy and isdescribed in U.S. Pat. Nos. 3,143,116 to A. I. Bates and 3,525,733 to I.K. Miller. Regeneration of such cyanoethylated viscose is accomplishedby use of a conventional acidic type coagulating and regenerating bath,as described above. Hydrolysis of the cyanoethyl group on the celluloseduring aging and processing produces predominately caboxyethylsubstituent groups on the cellulose in place of the cyanoethyl groups inthe resulting regenerated product. The term "regenerated cyanoethylcellulose" as employed herein refers to a regenerated product asproduced by the cyanoethylated viscose described.

Reference to the average degree of substitution (D.S) of the cyanoethylcellulose as used herein includes products wherein the anhydroglucoseunits of the cellulose molecules have an average substitution from about0.25 to about 0.65 of cyanoethyl groups or chemical groups derived fromsaid cyanoethyl groups by hydrolysis or other chemical change whichoccurs during manufacture and aging of the material. Thus, therecitation of cyanoethyl cellulose is also meant to include cellulosehaving carboxyethyl groups and some amidoethyl substituent groups.

EXAMPLE V

Example I was repeated, but instead of injecting thepolyvinylpyrrolidone alone there was injected a blend of equal volumesof a 9% solution of the polyvinylpyrrolidone in water with a 9% solutionof sodium carboxymethyl cellulose ("CMC") (Hercules grade 7 MF in 6%NaOH, D.S. of 0.7). Various amounts of this blend were used;specifically the proportions of cellulose; polyvinylpyrrolidone; andcarboxymethyl cellulose were varied as follows: 100:00, 95:2 1/2: 2 1/2;90:5:5; 85:7 1/2:7 1/2; 80:10:10. A portion of the resulting fibers wasfinished with a 1/2% water solution of Span 20 (sorbitan monolaurate);and then dried; a second portion was made somewhat alkaline by washingin 1% aqueous solution of sodium bicarbonate, then rinsed in waterbefore finishing with the 1/2% Span 20 solution and drying. The presenceof the additive gave improved fluid-holding capacity (measured by theSyngyna test as in Example III); for instance, the 80:10:10 blendtreated with sodium bicarbonate gave a fluid-holding capacity well above6 cc/g.

EXAMPLE VI

Example I was repeated, but instead of injecting polyvinylpyrrolidone("PVP") alone there was injected a blend of about 450 parts of a 6.7%aqueous solution of the polyvinylpyrrolidone K-90 and 550 parts of a5.5% aqueous alkaline solution of polyacrylic acid ("PAA"). The latterwas made by diluting 120 grams of Rohm & Haas "Acrysol A-5" (a 25%aqueous solution of a polyacrylic acid) with 338 ml of water, thenadding a stoichiometric amount of alkali, namely 92 grams of 18% aqueousNaOH solution. The K-90 solution was then added to the polyacrylatesolution with stirring and the resulting blend was a clear solutioncontaining about 3% of each of the polymers. Various amounts of theblend were used; specifically the proportions of cellulose;polyvinylpyrrolidone; polyacrylic acid; were varied as follows: 100:00,95:2 1/2; 90:5:5; 85:7 1/2: 7 1/2; 80:10:10. A portion of the resultingfibers was finished with a 1/2% water solution of Span 20 and thendried. A second portion was made somewhat alkaline by washing in a 1%aqueous solution of sodium bicarbonate, then rinsed in water beforefinishing with the 1/2% Span 20 solution and drying. The presence of theadditives gave improved fluid-holding capacity (measured by the Syngynatest as in Example III); for instance, the 90:5:5; 85:7 1/2: 7 1/2; and80:10:10 blends each gave a fluid-holding capacity well above 6 cc/g.

When the polyacrylic acid was only partially neutralized (e.g.neutralized with only 70% of the stoichiometric proportion of NaOH)before blending with the polyvinylpyrrolidone the improvement was not asmarked. Thus with 85 parts cellulose, 7 1/2parts PVP, 7 1/2 parts PAA(or 10 PVP and 5 PAA; or 5 PVP and 10 PAA) the fluid-holding capacitywas about 20-25% better than the control (100 cellulose) when suchpartially neutralized PAA was used. It is therefore preferred that theamount of alkali present in the system be at least equal to or greater(e.g. 20-30% greater) than the amount necessary to neutralize all theacidic groups of the added anionic polymer.

EXAMPLE VII

Example I was repeated except that the solution injected was prepared asfollows: A carboxyethyl starch ("CES") solution containing 9% starch wasprepared (see Ex. 1 of U.S. Pat. No. 3,847,636) with enoughacrylonitrile added to give a degree of substitution of 0.7. To a volumeof this solution was added an equal volume of 9% aqueous solution of PVPK-60. The resulting blend of polymer solutions (as tabulated in TableIV) was used for injection into viscose and subsequent spinning offibers. The fibers were processed as described in Example I. To oneportion a 1/2% Span 20 finish solution applied and then the fibers weredried. A second portion was immersed in 1% aqueous NaHCO₃, then in 1/2%Span 20 and dried.

The evaluation for fluid-holding by the Syngyna test gave results as setforth in Table IV.

EXAMPLE VIII

Example I was repeated with the following changes: The solutions forinjection into the viscose were prepared as follows. A carboxymethylstarch (CES) solution was prepared as stated in Example VII. Onesolution for injection comprised equal parts of the above CES solutionwith 9% aqueous PVP K-90. A second solution for injection comprisedthree parts of the above CES solution with one part of a 9% aqueoussolution of PVP K-90. Fibers were then spun by blending with viscose (astabulated in Table V). The fibers were processed as described in ExampleI and finished in an aqueous solution of 1/2% Na₂ HPO₄ and 1/2% Span 20.The results being given in Table V.

EXAMPLE IX

Using conventional rayon spinning equipment alloy rayon fibers wereproduced containing vinylmethylether-maleic copolymer andpolyvinylpyrrolidone K-90. Various blends, in proporations tabulated inTable VI below, were made of

(1) a 10% solution of the PVP K-90 (GAF Corporation), in water and

(2) a solution made by dissolving 100 parts of Gantrez AN-149 GAFCorporation (vinylmethylether-maleic anhydride copolymer) in a mixtureof 285 parts of 18% aqueous solution of NaOH and 626 parts of water(thus hydrolyzing and neutralizing anhydride groups of the copolymer).

The resulting blends were injected, as in Example I, into the viscosewhich was then extruded through a 980 hole spinneret into an aqueousspinning bath at 55° C. containing 7.2% H₂ SO₄, 22% Na₂ SO₄ and 0.6%ZnSO₄. The resulting tow was then stretched about 75% while passingthrough an aqueous bath containing 2 1/2% H₂ SO₄ at about 90° C., andformed into skeins. The skeins were washed in water at about 60° C. andcut to form staple fibers. One portion of the washed fibers (Samples A,B and C) was finished with 0.1% aqueous solution of Span 20 and dried atabout 70° C. A second portion of the washed fibers (Samples D, E and F)was treated with a half percent aqueous solution of NaOH, then washedwith softened water (which was slightly alkaline) then finished with a0.2% aqueous solution of Tween 20 and dried at about 70° C. Thetabulation in Table VI gives the proportions of the added ingredients,the results obtained in Syngyna Tests, and the pH values for 1% slurriesof the fibers in distilled water.

The more preferred fibers of this invention show a pH (measured in amixture of 100 parts distilled water and one part of fibers) of wellabove 6 and generally at least about 7, such as about 8, 9 or 9.5.

It is within the broader scope of this invention to employ in place ofall or part (e.g. 1/3, 1/2 or 2/3), of the polyvinylpyrrolidone, one ormore other N-vinyl amide polymers, e.g. N-vinyl lactam polymers,N-vinyl-2 of azolidinone polymers or N-vinyl-3-morpholinone polymerssuch as the polymers (including copolymers) listed in U.S. Pat. No.2,931,694, issued Apr. 5, 1960.

It will be noted that in the foregoing Examples, the fibers, as spun,are unpigmented and undyed. It is of course within the broader scope ofthe invention, although not at all necessary for practicing it, toincorporate pigment or dye into the spinning solution.

Fibers described in the above Examples had a denier per filament ofabout 3. It will be understood, of course, that the spinning may beeffected to produce other deniers such as 1.5, 4, 5.5 and 8 denier perfilament.

                  TABLE I                                                         ______________________________________                                                                  Fluid-Holding                                              Cellu-  Polyvinyl- Capacity  % Water                                   Sample lose    pyrrolidone                                                                              cc/g      Retention                                 ______________________________________                                        A      100      0         3.06      105                                       B      95       5         3.16      112                                       C      90      10         3.52      121                                       D      80      20         4.15      145                                       E      70      30         4.69      186                                       F      65      35         4.68      178                                       G      60      40         4.65      190                                       ______________________________________                                         % WATER RETENTION is the percent water retained by the loose mass of          fibers after centrifuging the same at 1000 G for 3.5 minutes.            

                  TABLE II                                                        ______________________________________                                                                        Fluid-Holding                                                     Polyvinyl-  Capacity                                      Sample   Cellulose  pyrrolidone cc/g                                          ______________________________________                                        J        100         0          4.36                                          K        90         10          4.84                                          L        85         15          5.38                                          M        80         20          5.46                                          N        75         25          5.65                                          ______________________________________                                    

                  TABLE III                                                       ______________________________________                                                                 Polyvinyl-                                                                             Fluid-Holding                               Sample Cellulose                                                                              CEC      pyrrolidone                                                                            Capacities cc/g.                            ______________________________________                                        A      100      0        0        3.06; 3.07;                                                                   3.14; 3.16                                  B      90       10       0        2.50; 2.55                                  C      80       20       0        2.95; 3.3                                   D      60       40       0        3.35; 3.5                                   E      90       0        10       3.52; 3.53                                  F      70       0        30       4.68; 4.70                                  G      75       12.5     12.5     5.03; 5.04                                  H      65       17.5     17.5     5.37; 5.39                                  ______________________________________                                    

                  TABLE IV                                                        ______________________________________                                                                 Fluid Holding Capacity                                      CES               cc/g                                                              (Expressed in     Without With                                   Sam- Cellu-  Terms of Starch   NaHCO.sub.3                                                                           NaHCO.sub.3                            ple  lose    Content)     PVP  Treatment                                                                             Treatment                              ______________________________________                                        A    100      0            0   4.3     4.0                                    B    90       5            5   4.8     4.2                                    C    80      10           10   4.7     5.2                                    D    70      15           15   4.9     5.2                                    ______________________________________                                    

                  TABLE V                                                         ______________________________________                                                      CES (Expressed                                                        Cellu-  in Terms of         Fluid Holding                               Sample                                                                              lose    Starch Content)                                                                              PVP  Capacity cc/g                               ______________________________________                                        A     100     0              0    4.08                                        B     89.2    5.4            5.4  4.80                                        C     80      10             10   5.44                                        D     80      15             5    5.40                                        E     89.2    8.1            2.7  4.80                                        ______________________________________                                    

                  TABLE VI                                                        ______________________________________                                        Sam-                                Fluid Holding                             ple  Cellulose                                                                              PVP    Gantrez AN-149                                                                           pH  Capacity cc/g                             ______________________________________                                        A    85.2     9.9    4.9        6.8 5.0                                       B    85.2     7.4    7.4        7.4 5.3                                       C    85.2     4.9    9.9        8.3 5.9                                       D    85.2     9.9    4.9        8.8 5.75                                      E    85.2     7.4    7.4        9.1 5.78                                      F    85.2     4.9    9.9        9.2 5.89                                      ______________________________________                                    

I claim:
 1. Alloy rayon fibers of higher fluid-holding capacity thannon-alloy rayon, comprising a regenerated cellulose matrix havingdispersed therein a polyvinylpyrrolidone polymer and an alkali metalsalt of a polyacrylic acid.
 2. Fibers as in claim 1 comprising aregenerated cellulose matrix having dispersed therein said salt of apolyacrylic acid selected from the group consisting of an alkalinesodium salt of acrylic acid homopolymer, of methacrylic acid homopolymerand of acrylic acid-methacrylic acid copolymers.
 3. Alloy fibersaccording to claim 1 wherein the added polymers are present in an amountsuch that the fibers have a fluid-holding capacity of at least 5cc/gram, as measured by the Snygyna test.
 4. Process of making thefibers of claim 1 wherein a blend of viscose with thepolyvinylpyrrolidone and the alkali metal salt of said polyacrylic acidis spun into a coagulating bath to form the fibers.